president obama has said he wants to prevent iran from getting nuclear weapons. but what does that mean in practice? and what the prime minister did today was say that for israel it's not the weapon that matters it is stopping them earlier than that. there's a point in the enrichment process that we have to stop them which injects clarity into the debate about the overall obctive. >> woodruff: so you're saying there was something new there? >> i think it's very useful that he helped clarify the israeli view that the definition of prevention, of stopping a nuclear weapon does not mean just before you turn the screw on the final device. it has to be to be effective it has to mean earlier in the enrichment process. >> woodruff: why is that significant? you started out saying you didn't hear anything new but maybe that is? >> we've been hearing about red lines for quite some time from the prime minister and he hasn't specified exactly what it is. it's been car to all that uranium ren itchment is the long poll in the tent. but i think he still left vague as to whether